| 09:30-10:40 | Fr1: Thermal transport, friction, and dissipation |
| 10:40-11:20 | Coffee break |
| 11:20-13:00 | Fr2: Catalysis and single-molecule chemistry |
| 13:00-14:00 | Closing session with poster prize ceremony, G. Benedek |
Chair: A. Mugarza, Barcelona, Spain
Contributed talk
Surface chemistry of metal oxide nanoparticles
Department of Chemistry, UMass Boston, Boston, MA 02125, USA
Understanding the surface chemistry of nanoparticles is vital to many fields, including clean energy production and storage, heterogeneous catalysis, materials chemistry, and environmental remediation. Nanoparticles are significantly more reactive than larger substrates due to their increased surface to volume ratio; however, the structural and electronic effects of nanoparticles do not necessarily mimic the macroscopic properties of the bulk material. Nanoparticles can be very difficult to characterize and it is challenging to elucidate their role as substrates in the reactions they are facilitating.
This project describes recent work focused on the surface chemistry of metal oxide nanoparticles, such as TiO2, ZnO, and ZrO2, commonly used in catalytic systems. In heterogeneous catalysis, these metal oxides are often used as a support medium for the catalyst and serve as an initial adsorption site for the molecules of interest. In photocatalytic systems, light induced reactions take place at the interface between the nanoparticle and an adsorbed sensitizing molecule. There are two primary classes of photocatalytic reactions: an adsorbate is excited by the light and interacts with the substrate, or the substrate is excited by the light and transfers an electron to the molecule. In both types of catalysis, it is the reaction of the adsorbate with the nanoparticle that truly drives the entire system. To maximize these catalytic processes, a better understanding of the interactions between the nanoparticles and the adsorbate is needed.
Unfortunately, using traditional surface science techniques to understand these reactions can be complicated. Traditionally in surface science, an investigator uses a well-defined substrate (single crystal, atomically smooth) in a controlled system (UHV, cryogenically cooled) to investigate reactions between the surface and an adsorbate of interest, thus isolating the interactions to be studied. However, studying the surface interactions on nanoparticles can be quite difficult due to the "materials gap", where the material used is not well-defined or characterized, and the "pressure gap", where the substrates are exposed to ambient conditions and reactions are performed either under high vacuum conditions or in the liquid phase.
Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) is well suited for analyzing the surface reactions on metal oxide nanoparticles. These particles are mostly transparent to the infrared and the multi-bounce nature of the diffuse reflectance helps to increase the signal from these low coverage reactions. Atomic Force Microscopy (AFM) is useful to monitor changes in nanoparticle morphology over the course of complex reactions. Confocal Raman Spectroscopy allows for the determination of structural variability, especially in the case of TiO2 which has different Raman spectra for the rutile and anatase phases. Together all of these tools have been used to monitor reactions and analyze product formation between the nanoparticles, both commercially available and synthesized, and a variety of probe molecules, such as acetic acid, formic acid, water and methanol, under different exposure conditions.